Analysis of reflectance difference spectra of Si(001)(2 x 1): As/Sb surfaces

We compute the surface dielectric function anisotropy (SDA) and reflectance -difference (RD) spectra of Si(001)(2 x 1):As/Sb surfaces. The calculations are based on the local density approximation (LDA) scheme and utilize a no vel set of basis functions, which are the products of plane waves in the su rface planes and localized Gaussian functions in the direction normal to th e surface. We identify and interpret the SDA and RD spectra in terms of int erband transitions, and find that these transitions are mainly related to t he electronic surface bands and surface-induced bands. Considering that the calculations based on the LDA of density functional theory (DFT) usually u nderestimate the band gaps for semiconductors, we make the many-body self-e nergy correction by shifting the related energy bands and then calculate th e dielectric function anisotropy and reflectance difference spectra. We als o take into consideration the excitonic and local field effects with a cont act-potential model. The final fitted result for Si(001)(2 x 1):As surface is in reasonable agreement with experimental observations. (C) 1999 Elsevie r Science B.V. All rights reserved.